This relates generally to integrated circuits, and more particularly, to integrated circuits with wireless communications circuitry.
Wireless integrated circuits such as transceiver circuits are sometimes configured to support complex, non-constant envelope modulation schemes such as the Wideband Code Division Multiple Access (W-CDMA) modulation scheme and the Orthogonal Frequency-Division Multiplexing Access (OFDMA) modulation scheme. High frequency signals generated using such types of radio access standards can exhibit high peak-to-average ratios (PARs), which can adversely impact the efficiency of radio-frequency power amplifiers used in wireless base transceiver stations (as an example). Reducing the PAR of these signals can help increase power amplifier efficiency and allows for higher average power to be transmitted.
In an effort to reduce signal PAR, a crest factor reduction (CFR) algorithm has been developed that involves iteratively cancelling unwanted signal peaks. In multi-standard applications, a CFR processor may simultaneously receive a first signal waveform associated with a first standard such as W-CDMA and a second signal waveform associated with a second standard such as OFDMA. The first and second waveforms are summed together prior to transmission with the power amplifier.
In a first scenario, peak cancellation operations are performed separately on the first and second waveforms prior to the waveforms being summed together. In this scenario, there is a chance that the first and second waveforms exhibit complementary peaks that actually cancel out with each other. In such cases, the peak cancellation being performed prior to the summation would be excessive. In a second scenario, peak cancelling operations are performed on the sum of the first and second waveforms. In this second scenario, there is a chance that the peak cancellation is subtracting power from the waveform with lower power contribution, which can result in unacceptably high error vector magnitude (EVM) degradation on the second waveform.